A turbine is provided with a turbine rotor blade, and a turbine housing having a scroll part extending along a circumferential direction of the turbine rotor blade. The scroll part is configured such that an A/R ratio of a flow passage area A to a distance R between an axis of the turbine rotor blade and a flow passage center of the scroll part has a concave distribution at least in a part of a graph where an abscissa represents a circumferential position around the axis of the turbine rotor blade and an ordinate represents the A/R ratio.